部分和问题

题目：给定整数a1,a2,..,an，判断是否可以从中选出若干数，使它们的和为k。n<=20

#include <iostream>using namespace std;int n,k,a[25];bool dfs(int i,int sum);void solve();int main(){    while(cin>>n){        for(int i=0;i<n;i++){            cin>>a[i];        }        cin>>k;        solve();    }    return 0;}void solve(){    if(dfs(0,0)) cout<<"yes\n";    else cout<<"no\n";}bool dfs(int i,int sum){    if(i==n) return sum==k;    if(dfs(i+1,sum)) return 1;    if(dfs(i+1,sum+a[i])) return 1;    return 0;}